I already filed my TAX, but I just realized there is a Premium Services Benefits add-on I didn't know about. HOW TO CANCEL THIS SERVICE? AND REFUND

That is the choice that allowed you to have your TurboTax fees deducted from your federal refund instead of paying upfront using a credit or debit card.   If you already e-filed your tax return it is too late to reverse that choice.

Are you in California?  Are you having the fees deducted from your refund?   If you are in California to remove the Premium Service you need to pay the fees upfront with a credit card.

https://ttlc.intuit.com/community/downgrading/help/how-do-i-remove-premium-services/00/26266